In general, a tool installed and used in a machine gradually incurs abrasion according to cutting machining to be finally damaged. The abrasion of the tool degrades quality of a processed surface, as well as numerical accuracy of a workpiece, and accidental damage of the tool may damage the workpiece. The aforementioned abrasion and damage of the tool may create monetary loss due to damage to the existing workpiece, and especially, is one of the primary causes of why unmanned processing is difficult in a CNC machine.
In order to solve the aforementioned problem, a tool lifespan management function has been recently developed to check a tool use time and automatically exchanges a tool in accordance with a predetermined use time. However, such a method is a method applicable to a case where a tool is used only under a specific processing condition in a mass production method, and is not applicable to a case where a different shape of component is processed each time.
In order to solve the problem, a technique of monitoring damage of a tool itself based on various measuring methods, such as an acoustic sensor, a cutting force sensor, and an image sensor is suggested.
However, since the technique of monitoring damage of a tool has an application limitation in an aspect of practical use according to a requirement of an additional measuring device, a method of detecting current signals from a servo and a spindle configuring a machine and monitoring damage to a tool based on the detected current signals has been most realistically used.
US Patent Application Publication No. 20060142893 suggests a method of determining damage to a tool by monitoring torque used for cutting machining through current signals from a servo and a spindle and checking a change in the torque according to passage of time and momentary displacement of a torque.
US Patent Application Publication No. 20060142893 includes, in order to perform monitoring damage to a tool, a detecting means for detecting indexes for a plurality of machining cycles, a comparing means for comparing an index in a specific machining cycle with existing index values in order to determine damage to the tool, a storage means for storing threshold values meaning the damage to the tool, a display means for writing an initial threshold value in the storage means, updating means for updating the stored values of the thresholds together while performing processing, a means for discontinuing the updating the values of the thresholds, and a determining means for determining set values of the thresholds based on the stored values of the thresholds when the update of the values of the thresholds is discontinued.
The technique of US Patent Application Publication No. 20060142893 is a practically useful method in an aspect that it is possible to detect damage to a tool through a current signal which is easily obtained without an additional device in a machine, and an appropriate threshold value is calculated in accordance with a processing situation without individually storing the values of the thresholds by a user.
However, the method has a problem in that it is impossible to recognize whether a change in torque generated by a change in a tool slowly progressing with the passage of time, such as abrasion of a tool, is a change by tool abrasion or a change by a change in a processing condition, and further, it is impossible to recognize whether, in view of the change of the processing condition, the change in the torque is generated by damage to the tool or an actual change in the processing condition.
Due to the aforementioned problems, the technique of US Patent Application Publication No. 20060142893 is disadvantageously and limitedly applicable only to a case in which processing under a uniform condition is repeated, for example, drilling of milling machining and tapping processing.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.